<!DOCTYPE HTML>
<html>
    <head>    
        <title>Example</title>
        <script>
            var toggleHidden = function() {
                var elem = document.getElementById("toggle");
                if (elem.hasAttribute("hidden")) {
                    elem.removeAttribute("hidden");
                } else {
                    elem.setAttribute("hidden", "hidden");
                }
            }
        </script>
    </head>
    <body>
        <button onclick="toggleHidden()">Toggle</button>
        <table>
            <tr><th>Name</th><th>City</th></tr>
            <tr><td>Adam Freeman</td><td>London</td></tr>
            <tr id="toggle" hidden><td>Joe Smith</td><td>New York</td></tr>
            <tr><td>Anne Jones</td><td>Paris</td></tr>
        </table>
    </body>
</html>
